DNS and WINS help you resolve names so you can connect to remote computers
across the LAN and across the Internet. WINS resolves computer (NetBIOS) names
such as \\surtur, and DNS resolves host names such as surtur.paradigms.com. To
help clarify some confusion surrounding the different types of name resolution,
this sidebar describes the steps a network takes to resolve computer and host
names.
Table A shows the properties for three computers in a TCP/IP network. (Note
that this network contains just one WINS server and is not the same network
described in the main article.) Two NT computers (\\patmos and \\samos) are in
one domain, and a Windows 95 computer (\\tadpole) logs in to that domain. In
this sample network, a WINS server runs on \\patmos, and \\samos and \\tadpole
point to that server to resolve NetBIOS names. DNS runs on \\patmos and \\samos,
and \\tadpole points to \\samos to resolve host names. Listing A shows the
contents of the DNS configuration files on \\patmos, and Listing B shows the
contents of the DNS configuration files on \\samos. Let's investigate both types
of name resolution.
NetBIOS Name Resolution
Clients resolve computer names such as
\\patmos and \\tadpole with NetBIOS name resolution. Suppose a user on the NT
server, \\samos, issues the command netusex:\\patmos\data
to display information about that computer connection. If you configure
\\samos to use WINS, host files, DNS, and lmhosts files, \\samos follows a
series of steps to resolve a computer name.
1. The \\samos server checks a local NetBIOS name cache for the \\patmos
computer name. If \\samos finds the name in the cache, it uses that cached name
to resolve the NetBIOS name.
2. If \\samos doesn't find a cached name, it tries three times to contact
the \\patmos WINS server. A WINS resolver on \\samos uses a hard-coded IP
address (204.241.138.10), rather than a NetBIOS or host name, in the TCP/IP
configuration so that the resolver can access the WINS server without needing to
know that the resolver is accessing \\patmos. The resolver's success in
accessing the WINS server depends on whether WINS is running on \\patmos and
whether the resolver finds a mapping (a correlation between the physical IP
address and computer name) in the WINS database for \\patmos. If the resolver
finds a \\patmos mapping, it uses that mapping.
3. If WINS is not running and the WINS resolution fails, \\samos tries
three times to resolve the name by sending out name query requests in
the form of broadcasts. Each computer on the network receives the broadcast and
checks its name cache to see whether this computer owns the nameif so, the
computer sends a name query response, using Address Resolution Protocol
(ARP) to obtain the source host's hardware address. This broadcast will succeed
on a local network such as our sample network but will fail in a routed
environment because most routers aren't configured to forward broadcasts.
4. If we add a router and the broadcasts fail, \\samos checks its local
lmhosts file for a \\patmos entry. If \\samos finds a \\patmos entry, it uses
that entry. Our sample network has no entry in \\samos's lmhosts file for
\\patmos.
5. If the lmhosts file lookup fails, \\samos tries a hosts file lookup.
Again, our sample network has no entry for \\patmos.
6. Finally, \\samos sends a request to its configured DNS, which is local
in this case. The resolution will work if the DNS completes a zone transfer from
the primary Domain Name Server for sakellariadis.com.
If we enter the same net use command from \\tadpole, we see a similar
series of events. The \\tadpole system will check its local files or send
requests to the WINS server at 204.241.138.10 or to DNS on \\samos.